1902 Encyclopedia > Ray


RAY. The Rays (Batoidei) together with the Sharks (Selackoidei) form the suborder Plagiostomata of Cartila-ginous fishes, and are divided into six families, as already noticed in ICHTHYOLOGY, vol. xii. pp. 685, 686.

The first family contains only the Saw-fishes (Pristis), of which five species are known, from tropical and subtropical seas. Although saw-fishes possess all the essential characteristics of the rays proper, they retain the elongate form of the body of sharks, the tail being excessively muscular am: "saw" (fig. 1) is a flat and enormously devel-oped prolongation of the snout, with an endo-skeleton which consists of from three to five carti-laginous tubes; these are, in fact, merely the rostral processes of the cranial cartilage and are found in all rays, though they are commonly much shorter. The integument of the saw is hard, covered with shagreen; and a series of strong teeth, sharp in front, and flat behind, are embedded in it, in alveolar sockets, on each side. The saw is a most formidable weapon of offence, by means of which the fish tears pieces of flesh off the body of its victim, or rips open its abdomen to feed on the organ of locomotion. The protruding intestines. The teeth proper, with which the mouth is armed, are ex-tremely small and obtuse, and unsuitable for inflicting wounds or seizing animals. Saw-fishes are abundant in the tropics; in their stomach & pieces of intestines and fragments of cuttle-fish have been found. They grow to SB' a large size, specimens with ==o saws 6 feet long and 1 foot 5=c broad at the base being of common occurrence. ^

The rays of the second CZ, family,


The third family, Torpedinidse, includes the Electric Eays. The peculiar organ (fig. 2) by which the electricity is produced has been described in vol. xii. p. 650. The fish uses this power voluntarily either to defend itself or to stun or kill the smaller animals on which it feeds. To receive the shock the object must complete the galvanic circuit by communicating with the fish at two distinct points, either directly or through the medium of some conducting body. The electric currents created in these fishes exercise all the other known powers of electricity : they render the needle mag-netic, decompose chemical -ompounds, and emit the spark. The dorsal surface of the electric organ is positive, the ventral negative. Shocks accidentally given to persons are severely felt, and, if pro-ceeding from a large healthy fish, will temporarily paralyse the arms of a strong man. The species of the genus Torpedo, six or seven in number, are distributed over the coasts of the Atlantic and Indian Ocean, and two reach northwards to the coasts of Great Britain (T. marmorata and T. hebetans). They are said to attain to a weight of from 80 to 100 lb, but fortunately such gigantic specimens are scarce, and prefer sandy ground at some distance from the shore, where they are not disturbed by the violent agitation of the surface-water. Other smaller size, inhabit different seas. All the rays of this family have, like electric fishes generally, a smooth and naked body.

The fourth family, Raiidm, comprises the Skates and Rays proper, or Raia. More than thirty species are known, chiefly from the temperate seas of both hemispheres, but much more numerously from the northern than the southern. A few species descend to a depth of nearly 600 fathoms, without, however, essentially differing from their surface congeners. Rays, as is sufficiently indicated by the shape of their body, are bottom-fishes, living on flat sandy ground, generally at no great distance from the coast or the surface. They lead a sedentary life, progressing, like the flat-fishes, by an undulatory motion of the greatly extended pectoral fins, the thin slender tail having entirely lost the function of an organ of locomo-tion, and acting merely as a rudder. They are carnivorous and feed exclusively on molluscs, crustaceans, and fishes. Some of the species possess a much larger and more pointed snout than the others, and are popularly distinguished as "skates." The follow-ing are known as inhabitants of the British seas :—(a) Short-snouted species: (1) the Thornback (R. elavata), (2) the Homelyn Ray (R. maeulata), (3) the Starry Ray (R. radiata), (4) the Sandy Ray [R. circidaris); (b) Long-snouted species, or Skates: (5) the Common Skate (R. batis), (6) the Flapper Skate (R. macrorhynchus), (7) the Burton Skate {R. marginatum), (8) and (9) the Shagreen Skates (R. vomer and R. fnllonica). A deep-sea species (R. hyper-borea) has recently been discovered near the Faroe Islands at 600 fathoms. Most of the skates and rays are eaten, except during the breeding season ; and even the young of the former are esteemed as food. The skates attain to a much larger size than the rays, viz., to a width of 6 feet and a weight of 400 and 500 lb.

The members of the fifth family, Trygonidee or Sting-rays, are distinguished from the rays proper by having the vertical fins replaced by a strong spine attached to the upper side of the tail. Some forty species are known, which inhabit tropical more than temperate seas. The spine is barbed on the sides and is a most effective weapon of defence ; by lashing the tail in every direction the sting-rays can inflict dangerous or at least extremely painful wounds. The danger arises from the lacerated nature of the wound as well as from the poisonous property of the mucus inoculated. Generally only one or two spines are developed. Sting-rays attain to about the same size as the skates and are eaten on the coasts of the Mediterranean and elsewhere. One species (Trygon pastinaca) is not rarely found in the North Atlantic and extends northwards to the coasts of Ireland, England, and Norway.

The rays of the sixth and last family, Myliobatidse, are popularly known under various names, such as "Devil-fishes," "Sea-devils," and '' Eagle-rays." In them the dilatation of the body, or rather the development of the pectoral fins, is carried to an extreme, whilst the tail is very thin and sometimes long like a whip-cord (fig. 3). Caudal spines are generally present and similar to those

FIG. 3.—Aetobatis narinari (Indo-Pacific Ocean).

of the sting-rays ; but in the pectoral fin a portion is detached and forms a " cephalic " lobe or pair of lobes in front of the snout. The dentition consists of perfectly flat molars, adapted for crushing hard substances. In some of the eagle-rays the molars are large and tessellated (fig. 4), in others extremely small. Of the twenty

FIG. 4.—Jaws of an Eagle-Ray, Myliobatis aquila.

species which are known, from tropical and temperate seas, the majority attain to a very large and some to an enormous size : one mentioned by Risso, which was taken at Messina, weighed 1250 lb. A foetus taken from the uterus of the mother (all eagle-rays are viviparous), captured at Jamaica and preserved in the British Museum, is 5 feet broad and weighed 20 lb. The mother measured 15 feet in width and as many in length, and was between 3 and 4 feet thick. At Jamaica, where these rays are well known under the name of " devil-fishes," they are frequently attacked for sport's sake, but their capture is uncertain and sometimes attended with danger. The eagle-ray of the Mediterranean (Myliobatis aquila) has strayed as far northwards as the south coast of England. (A. 0. G.)

The above article was written by: Albert Günther, M.D., Ph.D., F.R.S., Keeper of Zoological Department, British Museum.

About this EncyclopediaTop ContributorsAll ContributorsToday in History
Terms of UsePrivacyContact Us

© 2005-23 1902 Encyclopedia. All Rights Reserved.

This website is the free online Encyclopedia Britannica (9th Edition and 10th Edition) with added expert translations and commentaries